WO1992015995A1

WO1992015995A1 - New category of magnetic materials, their production and use

Info

Publication number: WO1992015995A1
Application number: PCT/EP1992/000433
Authority: WO
Inventors: Hans Juergen Richter; Ekkehard Schwab; Helmut Jakusch; Hartmut Hibst; Werner Grau; Eckhart Kneller; Reinhardt Hawig
Original assignee: Basf Aktiengesellschaft
Priority date: 1991-03-08
Filing date: 1992-02-28
Publication date: 1992-09-17
Also published as: JPH06505366A; DE59200858D1; EP0558691B1; ATE114866T1; EP0558691A1

Abstract

A new category of ferromagnetic materials consists of two phases, namely a hard magnetic phase and a soft magnetic phase, which are structured by interchange coupling of the spins of the two phases. Preferably the weak magnetic phase is of the cubic lattice type and the orientation of the hard magnetic phase is distributed statistically with respect to the principal direction of the soft magnetic phase. The magnetic material is characterized by high reversibility of the remanence and by an isotropic ratio of remanence to saturation magnetization greater than 0.6. A preferred embodiment of the material of the invention has the composition RExFeyBzSiuTv, where RE = rare earth and/or Y, Zr, Hf and T = Cr, Nb, Mo, V. The materials are suitable for permanent magnets, broadband microwave absorbers and magnetic recording media.

Description

A new category of magnetic materials, their manufacture and application description

The invention relates to a new category of ferromagnetic materials consisting of two phases with exchange coupling, wherein the composite material can have both a high saturation magnetization and a high coercive force as well as the production and use of these materials.

From DE 23 44 644 a magnetizable material with exchange anisotropy is known, consisting of a

Ferri- or ferromagnetic with an antiferromagnetic coupled to it. This material is characterized in that below a given temperature, which is lower than the Neel temperature of the antiferromagnetic, the critical magnetic field to be used for the irreversible rotation of the magnetization in the antiferromagnetic material and also the magnetic field for producing any magnetization structure, which leads to the irreversible rotation of the magnetization leads in the antiferromagnetic, are stronger than the strongest technically realizable recording magnetic field. As a result, all magnetization structures in magnetic fields that are smaller or the same as those generated by the strongest magnetic field disappear completely or partially after the generating magnetic field is switched off, such that signals previously fixed at a temperature above this temperature either regenerate themselves or partially or completely can be restored. This allows recordings to be made on a magnetic recording medium that are protected against subsequent unnoticed changes.

The present invention relates to a different principle of exchange coupling and to a correspondingly constructed ferromagnetic material, namely to a type of exchange spring mechanism. This combines two ferromagnetic phases, one magnetically hard and one magnetically soft. Magnetically hard materials generally have a high anisotropy with a relatively low saturation magnetization, while magnetically soft materials have a very large saturation magnetization and a very small anisotropy. By combining the two phases mentioned above through the exchange coupling, the advantages of both phases can be obtained simultaneously. An exchange spring magnet is thus characterized in that there is a coupling of the spins between the magnetically hard and the magnetically soft phase, which takes place either directly or through a coherence converter which conveys the coherence between the hard and soft magnetic phases.

In addition, it was found that ferromagnetic materials with a particularly typical exchange spring mechanism were obtained if the soft magnetic phase and / or the hard magnetic phase each consist of at least two partial phases. Such materials have a high isotropic remanence ratio M _r greater than 0.5 and a particularly high degree of reversibility in fields below M ^H c with a μ _{r of} the order of 5, which means that when a magnetic field is applied which is approximately equal to the coercive field strength the hard magnetic phase, practically the original remanence is reached again after removing the field. In order to obtain the desired high total magnetization, the volume fraction of the hard magnetic phase should generally be selected to be less than the fraction of the soft magnetic phase. However, since the necessary requirement for the presence of an exchange spring magnet is the exchange coupling between the magnetically hard and the magnetically soft

Phase, this depends on the distances between the hard magnetic inclusions and their dimensions themselves. It has been shown that for optimal implementation of the present invention, the distances between the hard magnetic inclusions should be of the same order of magnitude as the dimension of the inclusions themselves.

The hard magnetic phase and the soft magnetic phase result from coherent separation of a soft magnetic mother phase with a cubic structure, the orientation of the hard magnetic phase being statistically distributed on crystallographically equivalent axes of the mother phase. It was found that a magnet with exchange fe dere characteristics, is obtained with high coercive force and high saturation magnetization if the volume fraction of the soft magnetic phase is at least 30%, preferably at least 50% or greater. Among other things, the distribution of the volume fractions of hard and soft magnetic phases depends on the composition of the alloy.

To understand the spatial distribution of the hard magnetic inclusions in the soft magnetic matrix, one can use a model in which the hard magnetic inclusions sit like in a face-centered cubic grid on the corners and the center of a cube. Since hard magnetic materials generally generate strong crystal anisotropy through a corresponding crystal structure (e.g. hexagonal or tetragonal) and in addition there must be magnetic (and therefore crystallographic) coherence between the magnetically hard and soft phase, the crystal structures must be compatible with one another. Accordingly, e.g. an isotropic orientation of the hard magnetic inclusions in the soft magnetic matrix should not be magnetically coherent. Particularly favorable properties can be obtained with a cubic crystal structure of the soft magnetic matrix. In this case, due to the cubic symmetry, an excretion can be oriented crystallographically in several directions. The C-axes of the hard magnetic inclusions will be oriented parallel to the three (equivalent) crystal directions. For statistical reasons, the orientation of the hard magnetic inclusions is then divided equally between the excellent directions of the soft magnetic matrix, for example one third each on [100], [010] and [001]. In this way, the configuration mentioned above is formed, and each of the particles has no preferred magnetic axis. From these

Considerations immediately follow a possible isotropic ratio of the remanent to the saturation magnetization of greater than 0.5, preferably more than 0.6. In contrast, in a conventional magnet in which the anisotropy axes are distributed isotropically in the material by means of methods known from the prior art, only a ratio of remanence to saturation magnetization of 0.5 can be achieved. The most important characteristic of the exchange spring magnet is the extraordinarily high reversibility. This is understood here to mean that when a magnetic field is applied which is smaller than the coercive field strength of the hard magnetic phase, the original remanence is almost reached again after the field has been removed. This can apply even if the applied magnetic field is in the range of the coercive field strength of the hard magnetic phase. A simple one-dimensional model is shown in Figure 1. In the shaded areas there is the hard magnetic phase with a very large anisotropy constant, in the remaining area there is the soft magnetic phase with a very small anisotropy constant and a high saturation magnetization. When an opposing field is applied, the magnetization in the soft magnetic areas in

Field direction rotated (arrow), while the magnetization in the hard magnetic areas remains in its original position. So there is no magnetic reversal in the traditional sense, rather energy is pushed into the spin chain (exchange energy) by the external field. After switching off the field, the energy stored in the spin chain is completely recovered so that the exchange energy tries to smooth the spin structure again. This means that an extraordinarily high reversibility with partial magnetic reversal can be expected. The magnetization is only switched after a sufficiently high field strength has been reached. The exchange spring magnets typically have a μrev of greater than 2.5 (with large coercive field strengths), while conventional magnets have a μrev of 1-2. μrev is defined by the equation

ΔB = μo · μ _rev · ΔH.

It has been found that the exchange spring magnet is clearly characterized by the fact that in the composite material after previous magnetic saturation in one direction upon application of an opposing field, which is equal to the coercive field strength of the magnetic material, after removal of the field, at least 65% of the original saturation remanence can be achieved, the saturation remanence being at least 50% of the saturation magnetization. For this purpose, reference is made to FIGS. 2-3, in which the magnetization curve is shown. After magnetization in field H, the saturation magnetization 1% is reached and after removal of the field in point (1,1 '), the saturation remanence Mrs is reached. If an opposing field H = -H _c of the size of the coercive field strength is then applied, the material traverses curve A up to point 2.2 ', where it is demagnetized (M = 0). If the opposing field is removed (H = 0), point 3 'is reached with a magnet according to the prior art (curve C), in which a part of the remanent magnetization Mr is recovered, however

M _r / M _s <0.65.

In the case of a magnet with spring exchange properties, on the other hand, point 3 is reached on curve B, M _r / M _s > 0.65 being evident.

It has been found that a material with spring exchange properties is represented by an alloy which consists of at least two ferromagnetic and / or ferrimagnetic phases and which can have the following structure:

RE _x Fe _y B _z Si _u T _v , where RE = one or more elements selected from rare earths (Ce, Pr, Nd, Sm, Eu, Cd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and / or Y, Zr. and Hf and where

T = one or more transition elements with a body-centered cubic structure (Cr, Nb, Mo, V) and where x is not more than 10 atom% y is not more than 85 atom% z is not more than 25 atom% and is not more than 10 atom% v is not more than 10 atomic%. With such a composition, the coercive field strength can be varied within wide limits and selected to a desired value by selecting the rare earth component RE without the saturation magnetization and the isotropic remanence being significantly changed.

In addition, by selecting the transition metal component T, the saturation magnetization can be varied by up to about 50% and set to a desired value without the coercive field strength and the isotropic ratio of remanence to saturation magnetization being significantly changed.

Element V stabilizes the Fe23B6 phase; Si causes the formation and stabilization of the hard magnetic phase.

The magnetic material according to the invention just mentioned can be produced as follows. A melt consisting of RE, Fe, T, Si and B, the stoichiometric ratio of which determines the composition of the end product, is sprayed onto a rotating metal roller; the resulting amorphous flakes can, if necessary, be used in a grinding device which is known from the prior art be ground to the desired grain size. The desired ratio of hard magnetic to soft magnetic phase must then be set by annealing, preferably in the range from 670 to 780 ° C. for four to ten minutes.

Another method is mechanical alloying, in which the above composition is intensively ground for several days in a ball mill, for example with steel balls, and then tempered under an inert gas atmosphere. example 1

(Production example of magnetic material of the invention) A sample of the composition Nd _3.8 Fe _73.3 V ₃ B ₉ Si _18.0 _1.0 (specified in each case in atomic%) is brought to a temperature of 1250 ° C. The liquid material is placed on a copper roller with a diameter of 15 cm, which rotates at 4300 rpm, sprayed. The resulting amorphous tinsel are annealed, namely

Sample 1: 5 minutes at 708 ° C

Sample 2: 5 minutes at 725 ° C

Sample 3: 5 minutes at 775 ° C.

Figure 4 shows the measurement curve obtained with sample 2, namely hysteresis curve (1) and remanence curve (2). The samples have the magnetic characteristics listed in Table 1 below.

Table 1

Characteristic of the materials according to the invention is the high M _R / M _s ratio combined with high magnetization and the large ratio of remanent to normal coercive force, as can be seen from Table 1 and from Figure 2.

Mixtures of the composition α-iron and Nd ₂ Fe ₁₄ B were also used as materials with the exchange coupling described

Fe ₂₃ B ₆ and Y ₂ Fe ₁₄ B found.

A material according to the invention with an exchange spring action with the composition of the above example was compared with a conventional magnet based on NdFeB. Table 2 shows the comparison of the magnetic key figures: Table 2

The measurement was carried out with a vibration magnetometer at a maximum field strength of + 1592 kA / m and at room temperature.

Furthermore, the corrosion resistance was measured with both materials by storing the materials for 1 hour or 60 hours in a climate of 80 ° C. and 80% relative atmospheric humidity. This resulted in the following changes Δ (%) in the magnetic properties, namely coercive force and saturation magnetization

The following are further examples with the composition according to the invention and the magnetic characteristics. The melts specified in Examples 2 to 5 (element distribution in atom%) were sprayed onto a rotating metal roller as described and the amorphous flakes formed were each annealed at 700 ° C. for a few minutes. M _{r is} measured at H = 0 after the material has previously been demagnetized with -H _c (FIG. 3). Example 2

Nd _3.8 V _3.9 Si _1.0 B ₁₈ Fe _73.3-v Nb _v

Example 3

Nd _3.8 V _3.9 Si _1.0 B ₁₈ Fe _73.3-v MO _v

Example 4

Nd _3.8 Si _1.0 B ₁₈ Fe _77.2-v Mo _v

Example 5

Nd _3.8 V _{3. 9} Six. oB ₁₈ Fe _73.3 - _v Cr _v

As already stated above, a melt consisting of the specified alloy is sprayed onto a rotating metal roller. It has been found that metallic flakes formed by suitable selection of the rotation speed of the roller obtain the magnetic properties desired in each case. Subsequent annealing is not necessary.

Example 6

A melt of the composition Nd _9.5 Fe ₈₅ Si ₁ B _{4, 5} was sprayed onto a rotating copper roller with a circumference of 20 cm, which was 2000 or 3000.bzw. 4000 revolutions / min. rotates. FIG. 6 shows the magnetization curves obtained with these compositions, where mean

6.1.2000 rpm

6.2.3000 rpm

6.3.4000 rpm

From the curves it can be seen that at 2000 rpm. a material with useful properties is obtained.

Example 7

A melt of the composition Nd _9.5 Fe ₇₉ V ₅ Si ₂ B _4.5 was used as in Example 2.

In Figure 7 mean

7.1.2000 rpm

7.2.3000 rpm 7.3. 4000 rpm

At 3000 rpm. a material with useful properties is obtained.

Example 8

A melt of the composition Nd ₆ Fe ₈₅ Ni ₃ B ₆ is at 4400 revolutions / min. rotating copper wheel sprayed. The resulting tinsel have magnetic exchange spring mechanism properties. The magnetic data were measured, and what has already been said above applies to the measurement of M _r .

M ₂ = 170 Am ² / kg

H _c = 120 kA / m

M _rs / M _s = 0.70

M _r / M _rs = 0, 74 Example 9

A ferromagnetic alloy of the composition

Nd _3.8 Fe _77.2 B ₁₉ was produced (alloy A) as described above and ground to the desired grain size. The composite was then held at one for ten minutes

Annealed temperature of 675 ° C. The coercive force reached was M ^H c = 160 kA / m. Through continuous observation using X-ray structure analysis technology (DTXD = Dynamic Temperature X-Ray Diffraction) it was found that the soft magnetic phase initially consists of Fe ₂₃ B ₆ and then breaks down into Fe ₃ B and α-Fe.

Example 10 An alloy of the composition Nd _3.8 Fe _73.3 Bi _8.0 Si _1.0 V _3.9

(Alloy B) was prepared as described above and annealed at 675 ° C for 10 minutes.

It was determined by DTXD technology that the composite consisted of 90% soft magnetic phase and 10% hard magnetic phase. The soft magnetic phase consists of the two partial phases Fe ₂₃ B ₆ and Fe ₃ B, the hard magnetic phase be consists of Nd ₂ Fe ₁₄ B. The composite has a coercive force of M ^H c = 200 kA / m.

Example 11

An alloy of the composition as in Example 10 was produced and then annealed at 715 ° C. for 10 minutes. This time the composite consists of 80% soft magnetic phase, which contains the partial phases Fe ₂₃ B ₆ and Fe ₃ B and 20% hard magnetic phase (Nd ₂ Fe ₁₄ B). The coercive force is 300 kA / m. After applying a saturation field of 1200 kA / m, an m _R = M _R / M _S of 0.76 was measured, the μ _r value (μ _r - = 1 + M / H) was 5. Example 12

A composition as in Example 10 was annealed at 775 ° C for 10 minutes. The soft magnetic phase consists of the partial phases α-Fe and Fe ₃ B, the hard magnetic phase consists of Nd ₂ Fei ₄ B. The coercive force is 150 kA / m.

In summary, it can be said that in the case of a melt consisting of RE, Fe, B, Si, and T, the stoichiometric ratio of which determines the composition of the end product, and which is sprayed onto a rotating metal roller in an inert gas atmosphere The amorphous feed thus obtained is tempered in the range from 650 to 780 ° C. to set the desired phases, the dispersion of the phases, the compositions of the phases and the ratio of hard magnetic to soft magnetic phases, which overall determine the magnetic properties. Alternatively, the speed of rotation of the metal roller can be chosen so that the resulting crystalline flakes have the desired magnetic properties without subsequent annealing.

The following preferred applications have been found for the replacement spring magnets according to the invention, the invention not being restricted thereto. A) For permanent magnets

Permanent magnets based on AlNiCo, rare earth cobalt, NdFeB or hard ferrite are used as permanent magnetic excitation, for example for electric motors and generators. While the AlNiCo alloy is characterized by a high magnetization and a small coercive field strength, in the case of hard ferrite there is the reverse case of a high coercive field strength with a small magnetization. in the

In the case of the rare earth compounds, the magnetization with a sometimes very large coercive field strength is indeed much larger than with ferrite, but remains significantly smaller than with soft magnetic compounds or AlNiCo. The ability of a magnetic material to store energy is given directly by the maximum energy product, ie (BH) max. Under ideal conditions the maximum energy product is given by μ _o M _s ^2/4 , it is assumed that the coercive field strength is sufficiently large. A further increase in the coercive field strength beyond the value 0.5 M _s has no influence on the maximum energy product, the maximum energy product thus depends only on the saturation magnetization.

In order to be able to magnetically store as large as possible energies, a large magnetization with a sufficiently large coercive field strength of the magnetic material is therefore desirable. These two requirements are met by the material according to the invention, and some problems are avoided:

1. Since less rare earth is installed in the exchange spring magnet than in a conventional NdFeB or SmCo magnet, the material according to the invention is less expensive.

2. The properties of the composite can be set separately from one another by suitable selection of a soft and a hard magnetic material.

For example, the coercive field strength or the switching field strength can be set by the proportion of the hard phase The suitable choice of the soft phase, on the other hand, sets the saturation magnetization.

3. A suitable choice of the two components makes it possible to achieve a magnet with an extraordinarily high energy product. Due to the high magnetization, the maximum possible energy product μ _o M _s ² : 1.7 is significantly larger than that of a pure NdFeB magnet. The extraordinarily high reversibility significantly increases the dynamic energy product, which in the case of conventional magnets is significantly smaller than the static one. In practical operation, for example, a synchronous machine occurs due to the different magnetic lengths when the

Rotor, different degrees of demagnetization of the permanent magnet. In the case of a conventional magnet, starting from the most demagnetized operating state of the magnet, the operating state will be on a sub-loop, as shown in FIG. 5a. It can be seen that the demagnetization is largely irreversible. In contrast, demagnetization is almost completely reversible in the case of the novel exchange spring magnet (FIG. 5b), which immediately follows that a far higher dynamic energy product (BH) can be achieved.

4. With regard to the magnetization of a permanent magnet in a magnetic circuit, the problem of irreversible demagnetization occurs with a conventional magnet. This means that the magnet partially demagnetizes after being magnetized by removing it from the magnetization device (cf. FIG. 5a, point 1), which automatically results in an operating point on a sub-loop. When installed in an electrical machine, for example, the full potential is not developed. This disadvantage of a conventional magnet can only be countered by magnetization in, for example, the electrical machine, which, however, requires high energies. The exchange spring magnet according to the invention does not have this disadvantage. He can therefore be used in the magnetized state without irreversible loss. Due to the high magnetization, less magnetic volume is required to achieve a desired magnetic flux.

5. Due to the mode of operation of the exchange spring magnet, the size of the individual grains, as in a permanent magnet, is not relevant for the magnetic hardness, but only the microstructure of the soft and hard magnetic phases. There is therefore no need to construct a Peirmanent magnet from sufficiently small grains in order to obtain the desired magnetic properties. It follows, among other things, that corrosive influences, which are extraordinarily strong in the high-quality, rare earth-based magnets, are greatly reduced. In addition, the hard magnetic phase, which is susceptible to corrosion, is protected by a soft magnetic matrix which is less susceptible to corrosion.

6. The intrinsic isotropic properties of the material according to the invention provide direction-independent stability against external fields. This is particularly important for rotating machines, which naturally mean rotating magnetic fields and thus magnetic transverse loads on the permanent magnet. With conventional magnets, external fields in the transverse direction cause partially irreversible demagnetization, while these disadvantages do not arise with replacement spring magnets. 7. Since all hard magnetic materials first require a certain grain size in the range from less than 1 μm up to greater than 10 μm in order to achieve the hard magnetic properties, these materials are first pulverized or also produced directly as powder and then compacted by means of a sintering process. With these processes, it is difficult to achieve the mechanical dimensions accurately and to close complicated parts produce. Complicated molded parts can be obtained much more easily from plastics (e.g. polyethylene or polypropylene). For this reason, hard magnetic particles are embedded in the plastic mass in order to transfer the advantages to permanent magnets. You accept the resulting smaller magnetization, of course you will use a material with the highest possible magnetization as a filler so that the total magnetization of the plastic with its filling does not become too small. The material according to the invention is particularly suitable for this application, since it has a high magnetization and, above all, a high isotropic remanence. While conventional hard magnetic materials have to be aligned with a magnetic field within the plastic in order to obtain optimal properties, this process is not necessary when using an exchange spring magnet. Since an alignment process is usually not feasible, there is a great advantage of the exchange spring magnet. For magnetic recording media

Example 13

A magnetic recording medium is produced using the magnetic materials described in accordance with Samples 1-3 by the amorphous flakes being ground to a desired particle size in an inert gas atmosphere. The intrinsic properties of the resulting pigments are fully preserved. The pigments are then dispersed in a binder mixture consisting of a vinyl chloride-vinyl acetate copolymer and a polyester polyurethane, which are dissolved in an organic solvent, and applied to a polyester film in a magnetic field without alignment treatment and dried.

Signals in longitudinal track, helical track or vertical recording can be applied in an excellent manner to the magnetic recording medium thus obtained the; it is equally suitable for analog or digital signals. Such a material is particularly preferably suitable for disk media. By increasing the maximum achievable remanence compared to conventional magnetic pigments, a significantly higher reading signal is obtained. Furthermore, the dispersing behavior of the pigments in the binder solution is considerably more favorable than in the case of conventional magnetic pigments which are magnetically neutral immediately after production because, as stated above, the preferred axes of the magnetically hard phase are isotropically distributed in each particle.

Example 14

A melt with the composition Ce ₂ Fe ₁₄ B is processed as in Example 13. A magnetic recording medium is built up with the pigments obtained. As a result of Ce's low Curie point

(Tc = 435 ° K) the material obtained is ideally suited as a slave band for thermomagnetic duplication.

Examples 15 to 16 A melt of the composition as in Example 13 or 14 is applied by vacuum evaporation to a metallic substrate with a thickness of 0.3 μm. A magnetic medium for high-density longitudinal or vertical recording can be generated by annealing at 650 to 750 ° C. for 1 to 10 minutes.

Example 17

The procedure is similar to that in Examples 15 to 16, but the composition according to Example 1 or 2 is applied to a metallic substrate by sputtering. Here, too, a medium for high-density longitudinal or vertical recording is generated. The annealing treatment described above is of course not possible if the carrier material is thin

Plastic film, for example consisting of polyethylene terephthalate. With such magnetic The surface of the vapor-deposited layer or the layer applied by sputtering is brought to the desired distribution of hard and soft magnetic phases by brief irradiation in the range of a few ms with a laser beam or electron beam. The beam can scan ("wobble") the layer surface like a grid, similar to the so-called laser glazing known from the prior art, or the irradiation takes place over a large area with a so-called excimer laser. Depending on the intensity and the duration of the irradiation, only a part of the total layer thickness applied, ie the upper part, can obtain the desired spring exchange properties. This enables a reproducible, rational and quickly feasible production of thin-film media without heat treatment, even if these thin-film media have a layer thickness of less than 1 μm and if they have been vapor-deposited or sputtered onto thin substrates in the range of 3 - 150 μm.

The additional advantages for magnetic recording media achieved by the invention can be summarized as follows. 1) Due to the high reversibility with partial demagnetization, the reading signal is significantly higher. If the magnetic head magnetically shorts the medium during the reading process, the remanence almost rises to its original value. Conventional media have one due to the recoil mechanism described

Decrease in the read signal from normally 5 to 5 dB, which is inherently avoided in the medium according to the invention. 2) Since there is no preferred magnetic direction, isotropic remanence is always obtained since the alignment process is omitted. This is particularly favorable for disk media and hard disk media, in which alignment is undesirable, because otherwise the signal level

fluctuates. In this case, the use of a

Exchange spring magnets increase the reading signal compared to conventional media. Attention is also drawn once again to the favorable dispersing properties of the isotropic pigments in contrast to conventional fine-particle magnetic pigments, for example highly coercive acicular pigments. With these, there is always the problem in the magnetic dispersion of the reagglomerization of the pigments as a result of the mutual attraction, which must be solved by recipe and / or process measures.

3) Since the hysteresis curve is largely reversible, the read signal can be increased by using a current in the read head without affecting the written information. The reading current in the reading head only has to be such that field strengths are generated which are smaller than the switching field strength of the hard magnetic phase. In the case of a medium according to the prior art, the remanent magnetization is changed when an additional read current is used.

4) When the coercive field strength is reached, the recording medium according to the invention can also be demagnetized without external fields. In contrast to conventional media, the stored information is not lost because it remains stored in the exchange spring. The maximum recording density is therefore not determined by the demagnetization in the magnetic recording medium according to the invention.

5) There are also special advantages for metallic ones

Thin layers in which binder-free layers are produced by vapor deposition or sputtering. Conventional layers have a thickness of 0.2 - 0.3 μm and must have a sufficiently fine microstructure. This is typically columnar, so that the columns are ideally available as self-sufficient magnetic districts. Due to thermal stability problems (superparamagnetism), the particles in thin-film media cannot be made arbitrarily small. On the other hand, a thin film that is constructed with exchange spring magnets reacts completely differently. As already mentioned, this is not a one-domain behavior in the traditional sense. The storage takes place in principle in the hard magnetic inclusions, the soft magnetic matrix smoothes the magnetization. There the hard magnetic inclusions are very small, a very dense magnetic storage is possible despite the smoothing effect. Accordingly, a thin-film according to the invention behaves like an exchange-coupled traditional ferromagnetic layer that has an extremely fine microstructure. In addition, since demagnetization does not limit the storage capacity, there is therefore no need to use media that are as thin as possible for high-density longitudinal storage. In the case of a smaller writing depth than the layer thickness that occurs with a high writing density, the part of the magnetic layer which is not described acts due to the reversible permeability as a magnetic yoke. The magnetic yoke is also characterized by high reversibility, which means that the medium according to the invention will not completely demagnetize at a limited writing depth, because a magnetic yoke can be brought about by the non-magnetized part of the magnetic layer. In the case of perpendicular recording, the part that is not described automatically acts like a soft magnetic underlayer in a conventionally constructed magnetic recording medium. 6) For microwave absorbers

A ferromagnetic or ferrimagnetic material absorbs microwaves due to the ferromagnetic remanence.

In the case of single-domain particles, this absorption depends on the strength of the anisotropy field strength. For applications in the technically interesting area (e.g. shielding a microwave oven), anisotropy field strengths of around 80 kA / m must be available. One way of realizing such an absorption is accordingly to produce magnetic single domains with an anisotropy field strength of approximately 80 kA / m. In order to achieve a broadband effect, however, a wide distribution of the anisotropy field strengths is required according to the prior art.

In multi-domain particles, however, resonance of the domain walls is also possible. These resonance frequencies are at much lower frequencies, typically in MHz range. However, since there are only fragments of domain walls in an exchange spring magnet, on the one hand the resonance frequencies are significantly higher than with complete domain walls, on the other hand, however, there are domain wall pieces of very different sizes. The

The reason for this is that the angles between the easy axes in the hard magnetic areas are bridged by the magnetization in the soft magnetic phase. Since the positions of the hard magnetic preferred axes are different from each other, domain wall pieces of different sizes are created which have different natural frequencies. A broadband microwave absorber is obtained in this way. The magnetic material can be embedded in a plastic mass.

Claims

1. Magnetizable material consisting of at least two

Ferro- and / or ferrimagnetic phases exist which are magnetically coupled to one another by magnetic exchange coupling, characterized in that at least one of the phases is hard magnetic and at least one of the phases is soft magnetic, the volume fraction of the soft magnetic phase being at least 30% and being after previous magnetic Saturation in one direction when an opposing field is applied, which is equal to the coercive field strength of the magnetic material, after removal of the field, at least 65% of the original saturation remanence can be reached again, the saturation remanence being at least 50% of the saturation magnetization.

2. Magnetizable material according to claim 1, characterized in that the soft magnetic phase has a cubic structure and that the orientation of the hard magnetic phase is statistically distributed with respect to the main directions of the soft magnetic phase and the magnetic material has an isotropic ratio of remanence to Has saturation magnetization greater than 0.5, preferably greater than 0.6.

3. Magnetizable material according to claim 1, characterized by an alloy of RE _x Fe _y B _z Si _u T _v , where RE = one or more elements selected from rare earths (Ce, Pr, Nd, Sm, Eu, Cd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and / or Y, Zr and Hf and where T = one or more transition elements with a body-centered cubic structure (Cr, Nb, Mo, V) and where

x not more than 10 atomic%

y not more than 85 atomic%

z not more than 25 atomic%

u not more than 10 atomic%

v is not more than 10 atomic%.

4. Magnetizable material according to claims 1 to 3, characterized in that Fe up to 10 atom% is replaced by Ni and / or Co.

5. Magnetizable material according to claims 1 to 4, characterized in that the hard magnetic phase and / or the soft magnetic phase consists of at least two partial phases.

6. Magnetizable material according to claim 3, characterized in that the soft magnetic phase consists of the partial phases α-Fe and Fe ₃ B and that the hard magnetic phase has the composition Nd ₂ Fe ₁₄ B.

7. Magnetizable material according to claim 3, characterized in that the soft magnetic phase consists of the partial phases Fe ₂₃ B ₆ and Fe ₃ B and that the hard magnetic phase has the composition Nd ₂ Fe ₁₄ B.

8. A method for producing magnetizable material according to claim 3, characterized in that a

Melt consisting of RE, Fe, B, T and Si, the stoichiometric ratio of which determines the composition of the end product, is sprayed onto an rotating metal roller in an inert gas atmosphere and that the amorphous flakes formed are annealed in the range from 670 - 780 ° C to the desired temperature Ratio of hard magnetic to soft magnetic phase are brought.

9. A process for the preparation of magnetizable material according to claim 3, characterized in that a composition of RE, Fe, B, T and Si, the stoichiometric ratio of which determines the composition of the end product, intensively under an inert gas atmosphere in a grinding device ground (mechanical alloying) and then brought to the desired ratio of hard magnetic to soft magnetic phase by tempering in the range from 670 - 780 ° C.

10. A method for producing a magnetic recording material according to claims 8 or 9, characterized in that the composition in a fine dis Pergiereinrichtung finely ground to the desired grain size, then brought to the desired ratio of hard magnetic to soft magnetic phase by annealing in the range of 670 - 780 ° C and that the resulting magnetizable pigments together with polymeric binder on a substrate by a casting device without subsequent magnetic alignment of the pigments are applied.

11. A method for producing a magnetic recording medium with a material according to claims 1 to 3, characterized in that an alloy consisting of RE, Fe, B, T and Si, the stoichiometric ratio of which determines the composition of the end product, by evaporation in vacuo is applied to a layer support, whereupon the desired ratio of hard to soft magnetic phase is set by annealing the layer.

12. A method for producing a magnetic recording medium with a material according to claims 1 to 3, characterized in that a composition consisting of RE, Fe, B, T and Si, the stoichiometric ratio of which determines the composition of the end product, by sputtering is applied to a layer support, whereupon the desired ratio of hard to soft magnetic phase is set by annealing the layer.

13. A method for producing magnetizable material according to claims 1 to 3, characterized in that a melt consisting of RE, Fe, B, Si and T, the stoichiometric ratio of which determines the composition of the end product, is sprayed onto an rotating metal roller in an inert gas atmosphere and the speed of rotation of the metal roller is selected so that the resulting crystalline flakes have the desired magnetic properties without subsequent annealing.

14. A method for producing a magnetic recording medium with a material according to claims 1 to 3, characterized in that a composition Consisting of RE, Fe, B, T and Si, the stoichiometric ratio of which can be used to adjust the composition of the end product, is applied to a layer support by sputtering or vapor deposition, whereupon the layer surface is briefly treated in a grid pattern or over a large area with a laser beam or an electron beam.

15. Magnetic recording medium according to claims 1 to 13, characterized in that the magnetic recording medium is a hard disk, a floppy disk or a tape-shaped recording medium.

16. A magnetic recording medium according to claim 15, characterized in that RE = Ce and that the recording medium is used as a thermomagnetic duplicating material.

17. A method for producing a permanent magnet, characterized in that a material according to claims 1 to 6 is used.

18. A method for producing a permanent magnet, characterized in that a composition according to claims 1 to 6 is embedded in a plastic compound and potted.

19. Electron generator or electric motor, characterized in that the permanent magnetic excitation by a magnet according to claims 17 or 18.

20. absorber for microwaves, characterized in that the absorber has a composition according to claims 1 to 6 and 18.